A global trend towards the loss of evolutionarily unique species in mangrove ecosystems

The mangrove biome stands out as a distinct forest type at the interface between terrestrial, estuarine, and near-shore marine ecosystems. However, mangrove species are increasingly threatened and experiencing range contraction across the globe that requires urgent conservation action. Here, we assess the spatial distribution of mangrove species richness and evolutionary diversity, and evaluate potential predictors of global declines and risk of extinction. We found that human pressure, measured as the number of different uses associated with mangroves, correlated strongly, but negatively, with extinction probability, whereas species ages were the best predictor of global decline, explaining 15% of variation in extinction risk. Although the majority of mangrove species are categorised by the IUCN as Least Concern, our finding that the more threatened species also tend to be those that are more evolutionarily unique is of concern because their extinction would result in a greater loss of phylogenetic diversity. Finally, we identified biogeographic regions that are relatively species-poor but rich in evolutionary history, and suggest these regions deserve greater conservation priority. Our study provides phylogenetic information that is important for developing a unified management plan for mangrove ecosystems worldwide

A Global Trend towards the Loss of Evolutionarily Unique Species in Mangrove Ecosystems

Abstract The mangrove biome stands out as a distinct forest type at the interface between terrestrial, estuarine, and near-shore marine ecosystems. However, mangrove species are increasingly threatened and experiencing range contraction across the globe that requires urgent conservation action. Here, we assess the spatial distribution of mangrove species richness and evolutionary diversity, and evaluate potential predictors of global declines and risk of extinction. We found that human pressure, measured as the number of different uses associated with mangroves, correlated strongly, but negatively, with extinction probability, whereas species ages were the best predictor of global decline, explaining 15% of variation in extinction risk. Although the majority of mangrove species are categorised by the IUCN as Least Concern, our finding that the more threatened species also tend to be those that are more evolutionarily unique is of concern because their extinction would result in a greater loss of phylogenetic diversity. Finally, we identified biogeographic regions that are relatively species-poor but rich in evolutionary history, and suggest these regions deserve greater conservation priority. Our study provides phylogenetic information that is important for developing a unified management plan for mangrove ecosystems worldwide

Geographical distribution of species richness (A) and global decline (see Materials and Methods) (B) in mangrove ecosystems across six biogeographical regions, per quarter degree squares (QDS).

<p>Geographical distribution of species richness (A) and global decline (see Materials and Methods) (B) in mangrove ecosystems across six biogeographical regions, per quarter degree squares (QDS).</p

Model coefficients for the PGLS models of global decline in mangrove ecosystems.

<p>BL, terminal branch length; ED, evolutionary distinctiveness; H_max, maximum plant height. For all models the ML estimate of Lambda = 0.</p

Stacked histograms of the proportion of species declining globally when used for (A) structural building, and (B) forage.

<p>Stacked histograms of the proportion of species declining globally when used for (A) structural building, and (B) forage.</p

Model coefficients for the PGLS models of extinction risk in mangrove ecosystems.

<p>BL, terminal branch length; ED, evolutionary distinctiveness; H_max, maximum plant height. For all models the ML estimate of Lambda = 0.</p

Woody plant phylogenetic diversity supports nature's contributions to people but is at risk from human population growth.

The Tree of Life—phylogeny—provides a powerful tool for understanding the processes regulating life’s diversity. Conserving the branches on the Tree of Life might also have practical benefits. Using a comprehensive phylogeny of south ern African woody trees and shrubs, and structural equation modeling, we show that human population density correlates closely with not only the richness of woody plants in a region but also their evolutionary relatedness. Further, we demonstrate that more phylogenetically diverse species assemblages support a greater diversity of ecosystem goods and services. Our results suggest that peo ple in Africa may gain material benefits from inhabiting regions that support high phylogenetic diversity of woody plants. However, the correlation between human population and woody plant diversity creates a tension between people and biodiversity, which could threaten the contributions to people provided by intact and phylogenetically diverse ecosystems.This research was supported by the Government of Canada through Genome Canada and the Ontario Genomics Institute (2008-OGI-ICI-03), the University of Johannes burg, the South African National Research Foundation, the Royal Society (UK), and the Toyota South Africa through the Toyota Enviro Outreach Programme. KY was additionally supported by NRF grant #112113